1. Field of the Invention
The present invention relates to a color television image display apparatus equipped with an automatic image quality control means.
2. Description of the Prior Art
For the purpose of continuously achieving an optimal image state in television, technical development is progressing with regard to a television monitor having a function of automatically controlling the luminance, color saturation and so forth to optimal conditions in every field of a video signal. When the image being displayed in a television monitor changes momentarily among light, dark, colorful and nearly monochromatic states, it is impossible to achieve a desired optimal image condition continuously if the controls for the luminance, color saturation and so on are set at fixed positions. Therefore, a predetermined unitary amount of the video signal is analyzed and then the luminance control and others are adjusted in a manner to attain the best condition.
For example, as shown in FIG. 2, a video signal fed via a TV tuner 1 and an IF (intermediate frequency) amplifier 2 is supplied to an image quality control signal generator which comprises an A-D (analog-to-digital) converter 3 and an arithmetic processor 4 consisting of a microcomputer.
The arithmetic processor 4 sets, in each field of the video signal, sampling points denoted by S.sub.Pl -S.sub.Pn in FIG. 3 and supplies sample timing signals to the A-D converter 3. In accordance with such sample timing signals, the A-D converter 3 executes analog-to-digital conversion of the luminance signal, for example, and then outputs n digital data (voltage value data of the luminance signal) in every field to the arithmetic processor 4. Then the arithmetic processor 4 calculates one field of the luminance data and generates an image control signal S.sub.Al of the luminance amplification level in accordance with the result of such calculation (discrimination data determined by the lightness, darkness and so forth of the image). The image control signal S.sub.Al thus generated is supplied to a video signal processor 5 where the luminance amplification level is controlled, and the processed signal is outputted to a CRT display unit 6. Since such process is executed with regard to every field, it follows that an optimal image quality is ensured continuously.
According to the image quality control signal generator, it is possible to perform simultaneous adjustment of the color saturation, sharpness and so forth in addition to the luminance control by the same circuitry, hence achieving enhancement in the overall quality of the image being monitored.
However, in the conventional television image display apparatus mentioned above, there occurs a time loss which is required in the A-D converter 3 and the arithmetic processor 4 for generating an image quality control signal S.sub.Al to execute automatic image quality adjustment. Suppose now that, in an exemplary case where the arithmetic processor 4 consists of a 4-bit single chip microcomputer, a time of 0.1 second or so is required until an image quality control signal S.sub.Al(n) is outputted after sampling the data of one field F.sub.n. Then, at the instant the image quality control signal S.sub.Al(n) is inputted to the video signal processor 5, the video signal of a field F.sub.(n+5), which is posterior by 6 fields to the relevant field F.sub.n sampled for generating the image quality control signal S.sub.Al(n), is inputted to the video signal processor 5. Although it is a slight time delay, such delay causes a failure in adjusting the image quality of the field F.sub.n to be adjusted by the image quality control signal S.sub.Al(n).
Consequently, there arises a problem that when the image is suddenly changed, the image quality is deteriorated for a moment.